Brody Jenner, Avril Lavigne's Bloody Club Brawl: What Happened?

So what provoked a violent brawl involving Avril Lavigne and beau Brody Jenner (photographed early Monday with a bloody forehead) at a Hollywood club?

It's complicated.

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Both the singer, 27, and her reality star man, 28, tweeted late Monday about sparring with other revelers while out and about. Citing a black eye, bloody nose, bruises, cuts and ripped-out hair, Lavigne explained "I got attacked by 5 people last night out of nowhere. Not cool. My face is f----ed."

Added Hills alum (and Kim Kardashian's stepbrother) Jenner: "Interesting Saturday night... Just got of the hospital with a new scar on my face."

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One source tells Us the fight went down at Beacher's Madhouse, where Lavigne got into "an argument" with another woman.

Explains a second source: "At first, the girl called Brody something and that set Avril off so she talked s**t back to them."

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Observing the tiff, "Brody came over aggressively and got involved," the first source explains, adding that another man came to defend Lavigne's sparring partner. "They were scuffling on the floor...Brody was the aggressor and had five guys with him. When they finally got up Brody was bleeding."

Although many reports say Jenner was struck with a broken bottle, the first source says, "There was no bottle with blood and no bottle broken or anything like that [visible]."

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Jenner, Lavigne and their crew were eventually escorted off the property. Jenner later filed a police report for assault with a deadly weapon; the men with whom he fought did not press charges.